Economics, they've sold 70,000 less cars than 2015. If there are too many dealers the profits are going to hit several hard or reduce the potential closures and give them time to re-franchise. (If I remember correctly Mercedes did similar a few years ago).

2017 figures:
365 Vauxhall dealers sold 195,000 cars (534 units per dealer) in comparison 120 Kia dealers sold 93,000 cars (775 units per dealer).

It makes me laugh that manufacturers are reducing labour times for repairs/servicing, but dealers then put the labour rates up to cover the costs, either way the customer pays!